CHAPTER 6: SETPOINTS
S2 SYSTEM SETUP
345 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
6–53
Figure 13: Phasors for ABC sequence
Note that the delta winding currents lag the wye winding currents by 30°, which is in
agreement with the transformer nameplate.
Now assume that a source, with a sequence of ACB is connected to transformer terminals
A, C, B respectively. The currents that would be present for a balanced load are shown
below:
Figure 14: Phasors for ACB sequence
Note that the delta winding currents leads the wye winding currents by 30°, (which is a
type Yd11 in IEC nomenclature and a type Y/d330 in GE Multilin nomenclature) which is in
disagreement with the transformer nameplate. This is because the physical connections
and hence the equations used to calculate current for the delta winding have not changed.
The transformer nameplate phase relationship information is only correct for a stated
phase sequence.
It may be suggested that for the ACB sequence the phase relationship can be returned to
that shown on the transformer nameplate by connecting source phases A, B and C to
transformer terminals A, C, and B respectively. This will restore the nameplate phase shifts
but will cause incorrect identification of phases B and C within the relay, and is therefore
not recommended.
897717A1.CDR
828718A1.CDR